24,249 reputation
155129
bio website lightandmatter.com
location Fullerton, California
age
visits member for 3 years, 3 months
seen 20 hours ago

I teach physics at Fullerton College, a community college in Southern California. I have an undergrad degree in math and physics from Berkeley and a PhD in physics from Yale. Back when I was doing research, my field was experimental low-energy nuclear physics.


20h
comment Is superposition principle equally valid for both scalar and vector quantities?
@AlfredCentauri: The linearity of vector spaces as a matter of definition simply means that we have a clear definition of what it would mean for superposition to hold for a vector field. It doesn't mean that it does hold. For example, sound waves can be describes as a vector field, if you use a vector to describe the displacement. But sound waves only approximately superpose.
20h
comment Which nucleus is the most resilient against gamma-induced fission?
The definition in the question would include processes that I don't think any nuclear physicist would call fission, such as knocking out a single neutron. Generally we don't call it fission unless both of the products are heavier than alpha particles.
20h
comment Which nucleus is the most resilient against gamma-induced fission?
I don't think this is the right criterion. Being strongly bound is not the same as being non-fissile.
20h
comment Concerning the transtition between matter dominated universe and radiation dominated universe
@Gödel: By scale factor equations, do you mean the Friedmann equations? The Friedmann equations are simpler when there is only one form of matter present, so textbooks often present those simpler cases. That doesn't mean that realistic cosmological models only use the simpler versions.
1d
comment Covariant Nonlinear Transformation in two inertial frames
Is the matrix 4x4 still if you know its solution keeps always Real? I don't understand this sentence.
1d
comment Covariant Nonlinear Transformation in two inertial frames
I started to think what would the matrix be for any nonlinear transformation. Matrices are linear operators. You can't represent a nonlinear transformation with a matrix.
1d
comment Covariant Nonlinear Transformation in two inertial frames
What book is this from?
1d
comment If friction disregard area, why the direction you drag a long object matters?
related: physics.stackexchange.com/a/29954/4552
1d
comment If friction disregard area, why the direction you drag a long object matters?
I tried the experiment with the ruler, and I couldn't feel any clear difference.
1d
comment Why are objects at rest in motion through spacetime at the speed of light?
This has nothing to do with the question.
1d
comment What conditions should be met to notice a Doppler effect on light?
I don't get it. Where does the 3 come from?
2d
comment How can Lorentz contraction be “directly” measured?
There are plenty of high-precision experiments that show relativistic effects without the necessity of accelerating anything to a significant fraction of $c$. A good example is the famous Hafele-Keating experiment.
2d
comment At what velocity does space no longer equal a vacuum?
You're referring to a science fiction novel. The physics you're describing is made up.
2d
comment Black hole “no hair” theorem
Electric charge isn't quite as special as you're thinking. The no-hair theorems you usually hear about are for electrovac assumptions. So the special role of electric fields as opposed to any other fields is put in as an assumption. There are known counterexamples if you allow other fields. See livingreviews.org/lrr-1998-6 .
2d
comment Why GPS is at LEO?
@JerrySchirmer: That's not quite right. The usual goal is to locate yourself on a map, i.e., horizontally, and for that you get the best accuracy when the satellites are close to the horizon.
2d
comment Sound diffraction through a single slit
I wasn't the person who flagged it as low quality, but the original answer was only one sentence.
2d
comment Sound diffraction through a single slit
I don't think this is right, for the reasons given in my answer. Note that I gave three separate mechanisms for the diffraction to behave differently.
2d
comment Sound diffraction through a single slit
@Floris: You could also worry about the dielectric constant of the material, etc. You can't just assume a material with no electromagnetic properties -- such a material would be perfectly transparent.
2d
comment Sound diffraction through a single slit
related: physics.stackexchange.com/questions/5886/… physics.stackexchange.com/questions/141562/…
2d
comment Recommended books for undergraduate electrodynamics
@ChrisWhite: No way. Jackson has much more depth and breadth than Purcell. I learned E&M from Purcell as an undergrad and had Jackson in grad school, and there was a ton I learned from Jackson.